FORT EDWARD — As the first season of the nation's largest river-pollution cleanup project winds down, the biggest lesson learned has its roots in the Hudson River's long-ago heyday as a center for the logging industry.

Dredging of PCBs from the river bottom around Fort Edward ended at about 4 a.m. Tuesday, but crews will remain on the river for another couple of weeks, dumping clean soil and gravel into the river to patch over the dredged areas — a process comparable to laying down a new lawn to replace one that's been stripped away.

Next spring, scuba divers will start hand-planting aquatic plants on the new river bottom to speed up the restoration, said General Electric Co. spokesman Mark Behan. GE has been conducting the cleanup under the direction of the U.S. Environmental Protection Agency.

But between then and now, both EPA and GE will do their own studies on how the five months of dredging fared. That work will be judged by an independent panel of experts, who by next summer will assess the work and recommend any possible changes when dredging resumes in the spring of 2011.

A key issue is resuspension, which occurs when dredges scoop out PCB-laden muck. Some of the muck can be stirred back into the river and carried downstream. Work o the Hudson was slowed or stopped several times when PCB levels near the dredging spiked above safe levels — although levels remained safe further south, close to municipal drinking water intakes for Halfmoon and Waterford.

Some early lessons learned are that resuspension must be managed better and that dredging takes longer than expected, Behan said.

Even though GE dredged less acreage than planned, finishing only 10 of 18 mapped zones around Rogers Island, crews removed about 285,000 cubic yards of sediment, well beyond the goal of 265,000 cubic yards expected from all the zones.

That is because PCB pockets turned out to be between 60 percent and 80 percent larger than first thought, said Behan. These areas were obscured by a layer of logs, wood shavings and other debris left behind by the timber industry, which used the river to drive logs as well as to handle waste from paper mills upriver.

This debris also worsened the problem of PCB resuspension by preventing the dredge jaws from closing properly, which let some sediments spill back into the river.

Behan declined comment when asked whether the slower pace of work will raise the project's overall price tag, which GE has steadfastly refuse to disclose. Estimates earlier this year pegged the six-year project, which would cover about 40 miles of river as far south as Troy, at $460 million.

GE has paid about $629 million from 1990 through this spring for river studies and other work, Behan said, although the company has not committed to continue when dredging resumes.

The river cleanup is the largest project ever begun under the U.S. Superfund program. GE assembled a flotilla of 11 dredges, 17 tugboats, 20 barges and more than 400 rail cars as well as skiffs, cranes and other machinery. As many as 90 vessels were on the river each day.

Next year's study will aim at possible improvements to the work, said EPA spokeswoman Kris Scopeck. "Where we worked this summer was the most contaminated area," she said. "The debris field on the river bottom should be less prevalent further south, so the buckets should be better able to close."

Next year will be the year to study what was done and to suggest possible improvements, she said.

PCB-tainted sediment removed from the river was taken by barge to a facility on the Champlain Canal, where sediments were squeezed dry. Water was treated and pumped into the canal; the dried-out PCB sediments were shipped via rail cars to a toxic waste dump in Texas.